In accordance with this invention, unique Moirr deflectometry methods and equipment are used for both radiant deflection by refraction and reflection. The methods provide results that are on a par with Mach Zehnder interferometery. In both methods radiant deflection gratings or rulings are used to provide moire fringes. Deviations from the straight lines of the moire fringes are analysed to provide the sought-after quantitative measurements. Unlike conventional interferometery the methods to be described do not measure differences in optical length. Instead the method to be described measures deflections of beams away from the collimated pattern.
In comparison with interferometery, the moire deflectometry involves very simple alignment and therefore is much easier and less expensive to set up and nonetheless provides extremely reliable and accurate results.
The methods described herein do not require coherent light. The equipment comprises the two gratings, a collimated light source, a screen and a recording media. The methods are most attractive for low sensitivity measurements where the stability requirements of the moire deflectometry unlike those of interferometery are just one order of magnitude lower than the measured quantity. In contrast in interferometery the maximum permissible movement during the measurement is about .lambda./10. To maintain an upper limit of movement below this maximum is difficult and requires extremely specialized and sophisticated equipment.
There are many uses and therefore much need for reliable optical methods and equipment for analysing phase objects. Phase objects do not absorb or reflect light in general but change the phase of the light or deflect it. Examples of phase objects are such sundry items as lenses and even variations in the density of fluids which also cause the deflection of light. Thus, for example, equipment to analyze phase objects is useful for wind tunnels.
Prior art quantitative ways of detecting phase changes in beams caused by phase objects are well known interferometric technique as disclosed, for example, in the book entitled "Principles of Optics" by M. Born and E. Wolf published by Pergamon New York, 1970, on pages 256-370. The phase contrast method is also used to quantitatively determine the angular deflection in phase objects. Such prior art methods use difficult tuning steps and require high stability. The difficulties in meeting these criteria cause most phase objects to be analyzed optically by semi-qualitative methods such as the "Schlieren" photography method and "Shadowgraphy" such as described, for example, in the abovementioned "Principles of Optics" book at page 425.
The problem with semi-qualitative methods of phase-object analysis is that the actual quantities required are not provided. Thus, there is a dire need in the art for a reliable quantitative method and equipment for mapping phase objects capable of replacing the interferometric techniques. The quantitative method should be at least as easy to perform as "Schlieren" photography of Shadowgraphy and should provide highly reliable quantitative results.
In the past topographical analysis of surfaces such as those of mirrors and lenses, for example, have been made using interferometery and spectography. Such measurements are extremely delicate and require highly trained technicians using costly equipment and coherent energy sources. Thus the present methods in use suffer because of the high mechanical stability required. Accordingly costly and expensive equipment is required.
Accordingly it is an object of the present invention to provide new and improved methods and equipment for quantitatively mapping objects including phase objects through which the radiation passes and also the topography of a given surface which reflects the radiation, in which the above-referred to problems and disadvantages are substantially reduced or overcome.